In a standard IEEE 802.11a in a wireless LAN system communication is performed using a frequency band of 20 MHz per one channel. In a standard IEEE 802.11n or later, a channel bonding function of bundling a plurality of channels and performing communication is further stipulated. In the standard IEEE 802.11n, a maximum of two channels are bundled according to a situation where a channel is idled, and thus the communication can be performed using a frequency band of 40 MHz. In a standard IEEE 802.11ac, a maximum of eight channels are bundled, and thus the communication can be performed using a frequency band of 160 MHz. For example, as illustrated in FIG. 21, a primary channel is set and other channels that are bundled for use are set as secondary channels. Here, an example is described in which CH1 is intended to be a primary channel and CH2 to CH8 are intended to be secondary channels. Starting of transmission and reception in the AP and the STA is determined by carrier-sensing a signal on the primary channel. Whether or not the use of the secondary channel is possible is decided by whether or not another wireless station is using the channel.
Furthermore, in the standard IEEE 802.11ac, in order to improve efficiency of communication in a downlink direction from the AP to the STA, Multi-user multiple input multiple output (MU-MIMO) to which Spatial Division Multiple Access applies is employed, and it is possible that different wireless frames that are destined for a plurality of STAs are simultaneously transmitted from the AP. Additionally, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, in the wireless LAN system, in order to improve efficiency of access to many STAs, a technology in which the AP simultaneously transmits different wireless frames that are destined for a plurality of STAs using FDMA is considered.
However, in the STA that complies with the standard IEEE 802.11n or the standard IEEE 802.11ac, because transmission and reception necessarily needs to be performed using the primary channel, simultaneous transmissions that use FDMA may not be assumed. These STAs are referred to as legacy standard STAs. On the other hand, the STA in which the simultaneous transmissions that use FDMA are assumed is referred to as a new standard STA. Here, as illustrated in FIG. 1, when a legacy standard STA and new standard STA 1 to new standard STA 4 are connected to the AP, it is possible that new standard STAs or a combination of the legacy standard STA and the new standard STA performs the simultaneous transmissions that use FDMA. However, because the legacy standard STA necessarily uses the primary channel, the new standard STA is made to use a channel other than the primary channel.
FIG. 22 illustrates an example in which the AP performs the simultaneous transmissions that use FDMA to the legacy standard STA and the new standard STA. The present example is disclosed in Non-Patent Document 1. The new standard STA is expressed as a N-STA, and the legacy standard STA is expressed as a L-STA.
In FIG. 22, STAs that are connected to the AP correspond the following standards, respectively. An L-STA 1 (11a) supports only a primary channel CH1 in compliance with the standard IEEE 802.11a. An L-STA 2 (11n) supports the primary channel CH1 and a secondary channel CH2 in compliance with the standard IEEE 802.11n. An L-STA 3 (11ac) supports the primary channel CH1 and secondary channels CH2 to CH4 in compliance with the standard IEEE 802.11ac. However, because in these standards, the primary channel is necessarily used, the simultaneous transmissions that use FDMA are not assumed. However, in the standard IEEE 802.11ac, the simultaneous transmissions that use MU-MIMO are possible. On the other hand, it is assumed that an N-STA (11ax) complies with a new standard IEEE 802.11ax and, in addition to an IEEE 802.11ac function, performs the simultaneous transmissions which use FDMA.
With the configuration described above, the L-STAs cannot perform the simultaneous transmissions that use FDMA, but it is possible that a combination of the L-STA and the N-STA performs the simultaneous transmissions which use FDMA. However, when the transmission to a destination that is the N-STA is performed, a channel other than the primary channel CH1 is made to be used. In an example in FIG. 22, in the AP, a procedure in which pieces of transmission data that are destined for the L-STA 1 (11a) and the N-STA (11ax) occur and the simultaneous transmissions are performed is illustrated.
The AP transmits an RTS frame to a destination that is the N-STA (11ax), using all channels CH1 to CH4. The L-STA 1(11a), the L-STA 2 (11n), and the L-STA 3 (11ac) receive the RTS frame, which is not destined for the L-STA 1, the L-STA 2, and the L-STA 3 themselves, on the primary channel CH1, and set a NAV, a duration that is indicated in the RTS frame, for the primary channel CH1.
The N-STA (11ax) has a configuration in which carrier sense and demodulation are possible concurrently with each of the channels CH1 to CH4, and if the RTS frame in each channel, which results from the demodulation, is destined for the N-STA itself, returns the CTS frame to the AP using one or more, or all of the channels CH1 to CH4.
When receiving the CTS frame from the N-STA (11ax), the AP simultaneously transmits the data frame that is destined for the L-STA 1 (11a) and the N-STA (11ax), using FDMA. At this time, the AP performs the transmission to the L-STA 1 (11a), using only the primary channel CH1, and performs the transmission to the N-STA (11ax), using the channels CH3 and CH4, with the channel CH 2 being unoccupied as a guard band among the remaining channels CH2 to CH4.
When correctly receiving the data frame that is destined for each of the L-STA 1 (11a) and the N-STA (11ax) themselves, each of the L-STA 1 (11a) and the N-STA (11ax) replies with a block ACK (hereinafter referred to as a “BA”) on the channel on which the reception is performed.
Patent Document 1: Pamphlet of International Publication No. 2014/014084
Non-Patent Document 1: “Proposed Specification Framework for TGax” Robert Stacey et al., doc.:IEEE 802.11-14/1453r2, 5 Nov. 2014
Non-Patent Document 2: “Simultaneous Transmission Technologies for HEW” Koichi Ishihara et al., doc.:IEEE 11-13/1395r2, 12 Nov. 2013
Non-Patent Document 3: The LAN/MAN Standards Committee, “IEEE Std 802.11™-2012 IEEE Standard for Information Technology—Telecommunications and information exchange between systems—Local and metropolitan area networks Specific requirements Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” IEEE, 6 Feb. 2012